Abstract : A new approach is described for the inertialess 'TACAN Antenna System', using a new 'RADIAL DIRECTIONAL COUPLER' concept. A theoretical and experimental study is presented on the coupling of two radial lines. The coupling is obtained radially by means of uniform circular slots being infinitely thin, closely spaced and narrow. The anticipated use of the device resulted from the need of mixing various modes excited by two radial waveguide radiating elements. It is shown that in such devices, when excited by two radiating elements, the coupling is a function of the relative phase difference between the two inputs. It is also shown that when the phase is 90 degrees all the power appears at one of the mixing radiating elements, while maintaining a nominal 22 db of isolation between the exciting elements. A special configuration was selected for the antenna design using 4 and 36 current filaments in tow radial waveguides to produce the TEM, TM sub 10 and TM sub 90 fundamental modes. Theoretical and experimental study is also presented for this configuration including general discussion that outlines its influence on the Antenna System. A complete feed network design is presented employing stripline techniques to minimize the complexity of the multielements network. Experimental data contained herein, indicates a practical approach for an inertialess TACAN Antenna System. (Author)